The present invention relates to a universal joint to be used for, for example, a parallel link mechanism.
In prior art, there is known a parallel link mechanism in which a plurality of links are interposed between a base and an jolty table so as to allow the jolty table to perform a spatial motion.
FIG. 4 represents a driving simulation device utilizing such parallel link mechanism.
With reference to FIG. 4, a six actuators such as links 3 are disposed between the base 1 and the jolty table 2, and a jolt is imparted to the jolty table 2 by selectively expanding or contracting the respective actuators so as to control a cubic (i.e. three-dimensional) position and posture thereof. In this operation, the jolty table 2 has three degrees of freedom to determine the position thereof and three degrees of freedom to determine the posture thereof. And the jolty table has six degrees of freedom in total.
As a joint 4 interposed between both the end portions of the parallel link mechanism 3 and the base 1 or jolty table 2, there are known, as shown in FIGS. 5 and 6, a spherical bearing 5 allowing a spherical motion of the link 3 (FIG. 5) and a universal joint 6 allowing a variation of intersecting angle of the link 3 with respect to the base 1 or jolty table 2 (FIG. 6).
The spherical bearing 5 is a bearing supporting a spherical journal 7 provided for the end portion of the link 3 and has three degrees of rotational freedom, and because of this structure, the spherical bearing 5 can be smoothly operated at a time of determining the position and posture of the jolty table 2.
On the other hand, the universal joint 6 is composed of a known structure including a joint body 9 having a yoke 8, a cross fitting 10 and a bearing member disposed between the yoke 8 and the joint body 9, and such universal joint 6 has two degrees of rotational freedom.
Incidentally, in the parallel link mechanism, according to its own structure, an axial load of the link 3 is applied to the joint 4. With the spherical bearing 5 has a rigidity insufficient for supporting this axial load of the link 3. Moreover, in order to largely change the position and posture of the jolty table 2, it is necessary to make large an sway angle xcex1 of the link. However, in the spherical bearing 5, because the link 3 abuts against the bearing, it is difficult to make large this sway angle xcex1.
On the other hand, with the universal joint 6, it is possible to make large the sway angle xcex1 of the link 3. However, because the universal joint 6 has only two degrees of rotational freedom, the number of the degree of the rotational freedom is insufficient for finely determining the position and posture of the jolty table 2, and accordingly, there may cause a case that smooth operation for determining the position and posture of the jolty table 2 cannot be expected.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a universal joint for a parallel link mechanism capable of making smooth operation thereof, allowing a link to have a large sway angle and having a high rigidity to bear an axial load of the link.
This and other objects can be achieved according to the present invention by providing a universal joint comprising:
a first rotation guide means;
a second rotation guide means guided by the first rotation guide means to be rotatable; and
a third rotation guide means guided by the second rotation guide means to be rotatable, the first, second and third rotation guide means being operatively connected so as to provide three degrees of rotational freedom.
In a preferred embodiment, the first, second and third rotation guide means have rotational center lines, respectively, which intersect each other at one point.
The third rotation guide means guides a shaft member, of a mechanism to which the universal joint is applied, intersecting the rotational center line of the third rotation guide means at an acute angle, the rotational center lines of the second and third rotation guide means intersect each other at an acute angle, and a space is formed around the rotational center line of the third rotation guide means so that the shaft is allowed to turn full circle. In such case, the mechanism may preferably be a parallel link mechanism.
At least one of the first, second and third rotation guide means comprises an outer ring having an inner peripheral surface to which a V-shaped roller rolling groove is formed, an inner ring fitted to the outer ring and having an outer peripheral surface to which a V-shaped groove roller rolling groove is formed and a number of rollers accommodated in a roller rolling passage formed in combination between the roller rolling grooves so that rotation axes of adjacent rollers are normal to each other.
Furthermore, the operative connection of these rotation guide means is performed by a first connection member connecting the first and second rotation guide means and a second connection member connecting the second and third rotation guide means. The first connection member has a bowl shape having an edge portion to which the second rotation guide means is mounted, the edge portion having an inclined surface. The second connection member has a pair of connection pieces one of which has an inclined edge portion to which one surface of the third guide means is connected and another one of which has an inclined edge portion to which another surface of the third guide means is connected.
According to the structures and characters of the present invention mentioned above, since the universal joint has three degrees of rotational freedom, for example, when the universal joint is applied to a parallel link mechanism to determine posture and position of an jolty table of the mechanism, the universal joint can be smoothly and finely operated so that the link takes an optional three-dimensional position. Further, in this embodiment, each of the respective rotation guide means has one degree of rotational freedom, and for example, ball-and-roller bearing, thrust bearing, swiveling bearing, curvilinear guide means or the like may be utilized therefor.
In the preferred embodiment, since the first, second and third rotation guide means have rotational center lines, respectively, which intersect each other at one point, the posture of such as link can be effectively changed in the three-dimensional direction about the intersecting point being the center thereof.
Furthermore, in the preferred embodiment, the shaft of the link mechanism, for example, connected to the universal joint can be rotated by 360xc2x0, and hence, the wide sway angle of the shaft member can be ensured.
Still furthermore, according to the preferred embodiment, at least one of the first, second and third rotation guide means comprises an outer ring having an inner peripheral surface to which a V-shaped roller rolling groove is formed, an inner ring fitted to the outer ring and having an outer peripheral surface to which a V-shaped roller rolling groove is formed and a number of rollers accommodated in the roller rolling passage formed by these roller rolling grooves. When such example is applied to the parallel link mechanism, a mixed load of radial load, thrust load and moment load can be supported, thus providing high rigid structure of the universal joint.
Furthermore, since rollers have rolling contact between the V-shaped roller rolling grooves, and the inner and outer rings does not have sliding contact, it is not necessary to form any play between the inner and outer rings. And friction resistance due to the rolling motion of rollers is small, so that wearing (friction), heat or the like hardly occur, thus being advantageous.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.